Why slices are used in Go - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a slice of integers.

Go

var numbers [1]

Drag options to blanks, or click blank then click option'

Aint

B[5]int

Cmap[int]int

D[]int

Attempts:

3 left

💡 Hint

Common Mistakes

Using [5]int declares an array, not a slice.

Using int alone is just a single integer, not a slice.

In Go, slices are declared using [] followed by the type, like []int for a slice of integers.

2fill in blank

medium

Complete the code to create a slice from an array.

Go

arr := [5]int{1, 2, 3, 4, 5}
slice := arr[1]

Drag options to blanks, or click blank then click option'

A[1:4]

B[1]

C[:]

D[5]

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[1] returns a single element, not a slice.

Using arr[:] returns the whole array as a slice.

To create a slice from an array, use the slice expression with start and end indices like arr[1:4].

3fill in blank

hard

Fix the error in the code to append an element to a slice.

Go

var s []int
s = append(s, [1])

Drag options to blanks, or click blank then click option'

A5

B"5"

Cs

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an int causes a type error.

Trying to append the slice itself or the append function is incorrect.

The append function adds an integer value to the slice. The value must be an int, not a string.

4fill in blank

hard

Fill both blanks to create a slice with make and set its length.

Go

s := make([1], [2])

Drag options to blanks, or click blank then click option'

A[]int

B5

C10

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using int instead of []int for the slice type.

Confusing length with capacity.

The make function creates a slice of type []int with length 5.

5fill in blank

hard

Fill all three blanks to create a slice from an array and append a value.

Go

arr := [4]int{1, 2, 3, 4}
s := arr[1]
length := len(s) + [3]
s = append(s, [2])

Drag options to blanks, or click blank then click option'

A[1:3]

B5

C1

D[0:2]

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong slice indices that cause out of range errors.

Not updating length correctly after append.

The slice s is created from arr[1:3], then 5 is appended. The length is increased by 1 after append.

Practice

1.

Why are slices preferred over arrays in Go?

easy

A. Because arrays cannot store multiple values

B. Because slices use less memory than arrays

C. Because slices can change size dynamically while arrays have fixed size

D. Because slices are slower but more secure

Solution

1. Step 1: Understand array size behavior

   Arrays in Go have a fixed size defined at creation and cannot grow or shrink.

2. Step 2: Understand slice flexibility

   Slices are built on arrays but can dynamically change size, making them more flexible for varying data.

3. Final Answer:

   Because slices can change size dynamically while arrays have fixed size -> Option C

4. Quick Check:

   Slice size flexibility = A [OK]

Hint: Remember: slices grow, arrays don't [OK]

Common Mistakes:

• Thinking arrays can resize dynamically
• Confusing memory usage between slices and arrays
• Believing slices are slower than arrays

2.

Which of the following is the correct way to declare a slice of integers in Go?

var s _____

easy

A. []int

B. [5]int

C. int[]

D. slice int

Solution

1. Step 1: Recall slice syntax

   In Go, slices are declared with square brackets and no size: []type.

2. Step 2: Identify correct option

   []int uses []int which is the correct syntax for a slice of integers.

3. Final Answer:

   []int -> Option A

4. Quick Check:

   Slice declaration = []int [OK]

Hint: Slices use []type without size [OK]

Common Mistakes:

• Using fixed size like [5]int for slices
• Writing type after brackets like int[]
• Using invalid keywords like 'slice int'

3.

What will be the output of this Go code?

arr := [3]int{1, 2, 3}
slice := arr[:2]
slice = append(slice, 4)
fmt.Println(arr)

medium

A. [1 2 4]

B. [1 2 3 4]

C. [1 2 3]

D. Runtime error

Solution

1. Step 1: Understand slice and array relation

   The slice references the first two elements of arr: [1, 2], with length 2 and capacity 3.

2. Step 2: Append behavior on slice

   Appending 4 to slice: since current length 2 < capacity 3, it appends in place to the underlying array, setting arr[2] = 4. Thus, arr becomes [1 2 4].

3. Final Answer:

   [1 2 4] -> Option A

4. Quick Check:

   Append within capacity modifies underlying array = B [OK]

Hint: Append within capacity modifies shared array [OK]

Common Mistakes:

• Thinking append always reallocates a new array
• Expecting arr to grow to 4 elements
• Thinking append causes runtime error

4.

Identify the error in this Go code snippet:

var s []int
s[0] = 10
fmt.Println(s)

medium

A. Syntax error: slice declaration is incorrect

B. Slice s is nil and has no elements, so s[0] assignment causes runtime panic

C. No error, code prints [10]

D. Compile error: cannot assign to slice element

Solution

1. Step 1: Check slice initialization

   Variable s is declared but not initialized; it is nil with length 0.

2. Step 2: Understand assignment to s[0]

   Assigning to s[0] causes runtime panic because no elements exist yet.

3. Final Answer:

   Slice s is nil and has no elements, so s[0] assignment causes runtime panic -> Option B

4. Quick Check:

   Assigning to nil slice index = runtime panic [OK]

Hint: Initialize slice before assigning elements [OK]

Common Mistakes:

• Assuming slice auto-expands on index assignment
• Thinking code compiles with no error
• Confusing compile error with runtime panic

5.

You want to collect an unknown number of user scores efficiently. Which approach best uses slices?

1. Use a fixed-size array
2. Use a slice and append scores as they come
3. Use a map with indexes
4. Use a string to store scores

hard

A. Use a fixed-size array

B. Use a string to store scores

C. Use a map with indexes

D. Use a slice and append scores as they come

Solution

1. Step 1: Consider data size flexibility

   User scores count is unknown, so fixed-size array is not suitable.

2. Step 2: Evaluate slice usage

   Slices can grow dynamically and efficiently handle unknown data sizes by appending.

3. Step 3: Exclude other options

   Maps add overhead and strings are not suitable for numeric data storage.

4. Final Answer:

   Use a slice and append scores as they come -> Option D

5. Quick Check:

   Dynamic data collection = slice append [OK]

Hint: Use slices to grow lists dynamically [OK]

Common Mistakes:

• Choosing fixed arrays for unknown sizes
• Using strings for numeric data
• Overcomplicating with maps when slices suffice